Process for the production of graphite

Abstract

The application belongs to the technical field of nonmetallic materials, and particularly relates to a production process of graphite. The production process comprises the following steps: (1) calcining raw material needle coke, crushing and screening the needle coke to obtain granules and powder of different particle size grades; preparing a functional loading liquid, mixing the granules and powder of different particle size grades with the functional loading liquid respectively to obtain loading materials of different grades, wherein the functional loading liquid comprises an expansion inhibitor and boron-doped graphene; (2) mixing the loading materials of different grades, a binder and a lubricant to obtain a mixture; (3) extruding the mixture to obtain a green body; (4) baking the green body to obtain a baked body; and (5) graphitizing the baked body and performing mechanical processing to obtain graphite. The application solves the problem of irreversible expansion effect in the preparation of graphite by preparing a functional loading liquid and obtaining loading materials of different grades.

Description

Technical Field

[0001] This invention belongs to the field of non-metallic materials technology, specifically relating to a graphite production process. Background Technology

[0002] Graphite is a conductive material produced by a series of processes, including raw material calcination, crushing and screening, kneading, molding, primary roasting, impregnation with molten pitch followed by further roasting, graphitization, and machining. It has core characteristics such as high temperature resistance, excellent electrical and thermal conductivity, strong thermal shock resistance, and good chemical stability, making it an indispensable key consumable in the fields of high-temperature smelting and electrical processing.

[0003] In the production process of graphite materials, graphitization involves heating amorphous carbon blanks to an ultra-high temperature of 2800~3000℃, causing the amorphous carbon atoms in the carbon material to rearrange their crystal lattice and transform into a hexagonal graphite structure. Graphitization is a key process that determines the core properties of graphite, such as electrical conductivity, thermal conductivity, and thermal shock resistance.

[0004] In the aforementioned graphitization process, abnormal expansion (known in the industry as the Puffing effect) has long been a core technical challenge restricting the yield and performance of ultra-high power graphite materials. Specifically, when the graphitization temperature reaches the range of 1600~2200℃, the carbon blank exhibits irreversible abnormal volume expansion that deviates from the normal graphitization shrinkage trend. This phenomenon is particularly pronounced in ultra-high power graphite materials made from highly oriented needle coke. Furthermore, with the widespread adoption of series-heated (LWG) graphitization furnaces, the heating rate has increased significantly, compressing the gas escape time window and further exacerbating the probability and severity of the Puffing effect. The Puffing effect easily leads to the formation of numerous microcracks within the finished graphite material, reducing its mechanical strength, thermal shock resistance, and electrical conductivity uniformity.

[0005] Regarding the mechanism of the Puffing effect, current research generally considers it to be the result of multiple coupled factors, with the core causes summarized into two categories: First, the concentrated decomposition of sulfur to produce gas is the primary inducing factor. Approximately 70% of the sulfur in needle coke and petroleum coke is embedded in the carbon layer edges and lattice defect sites in the form of thiophene-type organic sulfur. The bond energy of the CS bond determines that it undergoes large-scale breakage in the 1600–2200℃ range, releasing sulfur atoms that combine to form gaseous molecules. However, the interior of the calcined carbon matrix is ​​predominantly a closed-pore structure, and the diffusion rate of gas molecules is far lower than the formation rate, leading to a sharp increase in internal pore pressure. When the internal pressure exceeds the high-temperature tensile strength of the carbon matrix at that temperature, it triggers pore expansion, microcrack initiation, and propagation. Second, sulfur atoms originally act as cross-linking points to constrain the relative slippage between carbon layers in graphite microcrystals. When sulfur atoms are removed, the cross-linking constraint between carbon layers disappears, and needle-shaped coke microcrystals can undergo irreversible warping and interlayer slippage, resulting in additional volume expansion. The higher the orientation degree of the needle-shaped coke, the more obvious the lattice distortion expansion effect is. This is the essential reason why the Puffing problem of ultra-high power graphite materials is more prominent than that of ordinary power graphite materials.

[0006] The current mainstream solution in the industry is to add single or simple compound inorganic sulfur inhibitors, such as calcium oxide, calcium carbonate, and iron oxide powders, during the kneading process. These powders react with sulfur to form solid sulfides, thereby reducing gas generation. For example, US Patent 3563705A discloses a method for suppressing expansion in graphite preparation. This method involves incorporating delayed expansion inhibitors, such as titanium or zirconium compounds, into a graphitizable mixture composed of sulfur-containing coke, binder, and conventional expansion inhibitors to eliminate the expansion of the graphitizable mixture caused by thermal sulfur release under graphitization conditions. For a typical sulfur-containing coke-asphalt mixture, which contains approximately 0.5 to 5 wt% or more of iron oxide as a conventional expansion inhibitor, the most effective concentration of titanium or zirconium compounds (calculated as TiO2 or ZrO2) is approximately 0.05 to 5 parts per 100 parts of coke.

[0007] For example, Chinese patent CN102363526A discloses an ultra-high power graphite electrode with a diameter of 650mm. This graphite electrode includes a dry material composed of large-particle oil-based needle coke, medium-particle oil-based needle coke, and small-particle powder, as well as binders, additives, raw crushed material, and calcined crushed material. The graphite electrode is manufactured through crushing and screening, batching, mixing, molding, calcination, impregnation, graphitization, and processing into a finished product. The dry material is calculated by weight percentage as follows: large-particle oil-based needle coke 45%, medium-particle oil-based needle coke 10%, small-particle powder 45%, binder accounting for 25-30% of the total weight of the dry material, stearic acid additive accounting for 0.5-0.8% of the total weight of the dry material, Fe2O3 iron powder additive accounting for 0.5% of the total weight of the dry material, raw crushed material accounting for 5% of the total weight of the dry material, and calcined crushed material accounting for 5% of the total weight of the dry material. The binder is modified asphalt. This patent addresses the challenge of producing large-size UHP electrodes from coal-based needle coke by mixing it with binder asphalt, additive stearic acid, and Fe2O3 iron powder.

[0008] However, in practical industrial applications, technical solutions like US3563705A and CN102363526A have several drawbacks: First, existing technologies only add inorganic powders such as iron oxide during the kneading process, making it difficult to achieve stable and uniform dispersion of the powders with pitch and coke particles; iron oxide powders are prone to agglomeration, forming large particles and significantly reducing the effective reaction area. Second, the iron oxide powder is randomly dispersed within the carbon matrix, and sulfur must diffuse through the bulk phase to reach the surface of the iron oxide particles, resulting in high mass transfer resistance and a slow reaction rate. Especially under the rapid heating conditions of the LWG furnace, there is a risk that the sulfur release rate will exceed the sulfur fixation reaction rate, which is not conducive to further suppressing the graphitization puffing effect. Summary of the Invention

[0009] The purpose of this invention is to provide a graphite production process to solve the problem of irreversible expansion effect, also known as the Puffing effect, during graphite preparation.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The graphite production process of this invention includes the following steps: (1) The raw material needle coke is calcined and then crushed and screened to obtain granules and powders of different particle sizes; a functional loading liquid is prepared, and the granules and powders of different particle sizes are independently mixed with the functional loading liquid for loading to obtain loading materials of each grade; the functional loading liquid includes expansion inhibitors and boron-doped graphene. (2) The load-bearing materials, binders and lubricants of each grade are mixed to obtain a mixture; (3) The mixture is extruded to form a green body; (4) The raw blank is baked to obtain the cooked blank; (5) The molten blank is graphitized and then processed into graphite.

[0011] in: In step (1), the calcination temperature is 1250~1350℃, and the calcination time is 20~30h; after calcination, the true density of the needle coke is ≥2.12g / cm³. 3 Resistivity ≤ 500 μΩ·m.

[0012] In step (1), after crushing and screening, four granular grades, namely granules A1, A2, A3 and A4, and two powder grades, namely powder B1 and B2, are obtained. The particle size range of granules A1 is 8mm≤A1<12mm, the particle size range of granules A2 is 4mm≤A2<8mm, the particle size range of granules A3 is 0.5mm≤A3<4mm, and the particle size range of granules A4 is 0.01mm≤A4<0.5mm. The particle size range of powder B1 is 0.075mm≤B1<0.15mm, and the particle size range of powder B2 is 0.01mm≤B2<0.075mm.

[0013] In step (1), the expansion inhibitor is iron oxide, and the functional loading liquid also includes melamine, polyethylene glycol, boric acid, and water. Based on 100 parts by mass of iron oxide, melamine is 9-12 parts, polyethylene glycol is 12-20 parts, boric acid is 9-18 parts, boron-doped graphene is 8-12 parts, and water is 600-800 parts. The boron-doped graphene is prepared by grinding graphene oxide and boric acid, followed by two heat treatments and washing. The mass ratio of graphene oxide to boric acid is 1:0.85-1.8. The first heat treatment temperature is 190-220℃, and the first heat treatment time is 20-30 min. The second heat treatment temperature is 400-430℃, the second heat treatment pressure is 12-15 MPa, and the second heat treatment time is 50-60 min.

[0014] In step (1), granules and powders of different particle sizes are independently mixed with functional loading liquid at a mass ratio of 1:0.08~0.1 and then loaded; granules A1, A2, A3, A4, powder B1 and powder B2 are independently mixed with functional loading liquid and loaded to obtain loaded materials A1, A2, A3, A4, B1 and B2.

[0015] In step (2), the binder is coal tar pitch and the lubricant is stearic acid. The composition of the ingredients by mass percentage is as follows: load material A1 accounts for 28~32wt%, load material A2 accounts for 10~16wt%, load material A3 accounts for 15~18wt%, load material A4 accounts for 6~12wt%, load material B1 accounts for 6~10wt%, load material B2 accounts for 4~8wt%, coal tar pitch accounts for 15~20wt%, and stearic acid accounts for 1.2~2.0wt%.

[0016] In step (2), the mixing includes dry mixing and wet mixing in sequence. The dry mixing temperature is 120~150℃ and the dry mixing time is 20~35min. The wet mixing pressure is -0.08~-0.05MPa, the wet mixing temperature is 170~190℃, and the wet mixing time is 40~55min. After wet mixing, the material is cooled down to 90~120℃ within 20~30min.

[0017] In step (3), the material is pre-pressed at 15-25 MPa for 3-5 minutes before extrusion molding; the extrusion temperature is 120-140℃, the extrusion pressure is 20-35 MPa, and the extrusion speed is 50-150 mm / min.

[0018] In step (4), the roasting includes primary roasting and secondary roasting after impregnation with coal tar pitch; during primary roasting, the temperature is raised to 1200℃ and held for 12-20 hours; during secondary roasting, the temperature is raised to 800℃ and held for 5-8 hours; preferably, the heat treatment curves for primary and secondary roasting are shown in the table below:

[0019] In step (5), graphitization is carried out in an LWG furnace with gradient heating. The gradient heating process is as follows: heating to 1500℃ at a heating rate of 15~25℃ / h and holding at that temperature for 1~2h; then heating to 2200℃ at a heating rate of 3~8℃ / h and holding at that temperature for 2~5h; finally heating to 2800℃ at a heating rate of 20~30℃ / h and holding at that temperature for 8~15h.

[0020] The beneficial effects of this invention are as follows: (1) During the load phase: Boric acid has a planar structure with three -OH groups uniformly distributed in the same plane. Melamine's triazine ring is a planar six-membered aromatic ring with three -NH2 groups uniformly distributed on it. The -OH groups of boric acid can form multiple hydrogen bonds with the triazine ring and -NH2 groups in melamine, forming a hydrogen-bonded network structure. This network structure is well-compatible with the two-dimensional honeycomb lattice structure of boron-doped graphene. The network structure can also interact with hydroxyl and carboxyl groups on the surface of boron-doped graphene through intermolecular interactions. Uniform mixing of the boron and nitrogen sources is achieved during the liquid-phase loading stage. The ether oxygen atoms in polyethylene glycol (PEG) can bind to the hydrogen-bonded network structure through hydrogen bonds and van der Waals forces, allowing the functional loading liquid to better conform to the curvature and defects of the needle coke surface. Furthermore, the flexible molecular segments in PEG give the functional loading liquid a certain degree of fluidity, resulting in a more uniform distribution of the functional loading liquid within the needle coke.

[0021] After loading, the boron-doped atoms on the surface of boron-doped graphene itself serve as seed crystals for the growth of the boron-nitrogen phase structure during subsequent calcination. Together with boric acid (the main boron source) and melamine in the functional loading solution, they prevent the disordered flow of boric acid and melamine during subsequent calcination, thus ensuring the calcination effect.

[0022] (2) During the roasting stage: Boric acid and melamine react at high temperatures to form melamine borate, which further generates a boron-nitrogen phase structure on the surface of boron-doped graphene. The boron-nitrogen phase structure grows on the graphene substrate to form a composite structure, which acts on the surface of needle coke. This helps iron oxide particles to pre-fix sulfur in the needle coke, thus fixing sulfur before it enters the high-temperature region of graphitization, thereby reducing the emission of gaseous sulfur substances during the graphitization stage from the source.

[0023] (3) During the graphitization stage: The composite structure offers several technical advantages in addressing the concentrated decomposition and gas generation mechanism of sulfur. First, boron-doped graphene is an excellent conductor, which facilitates the reduction process of iron oxide particles and pre-fixed sulfur elements during the graphitization stage, preventing sulfur accumulation. Second, it promotes contact between sulfur and iron oxide particles, rather than relying solely on bulk diffusion. Third, the composite structure can physically adsorb a portion of sulfur elements, acting as a buffer for sulfur storage. Through these three effects, the sulfur fixation reaction proceeds more smoothly, forming a synergistic inhibition of the concentrated decomposition and gas generation mechanism of sulfur.

[0024] In addition, after the removal of sulfur atoms, needle-shaped coke is prone to interlayer slip and warping due to the loss of cross-linking constraints, which leads to lattice distortion and expansion. In this invention, the composite structure is highly similar to the graphite layered arrangement structure. The composite structure itself acts as a two-dimensional rigid skeleton, which plays a role in spatial constraint, suppresses deformation, fundamentally curbs the occurrence of lattice distortion and expansion, and avoids the concentrated release of expansion stress.

[0025] The composite structure can alleviate the gas production caused by concentrated decomposition of sulfur and the expansion of needle coke caused by the removal of sulfur atoms, resulting in graphite with excellent mechanical strength (flexural strength and elastic modulus), thermal shock resistance (coefficient of thermal expansion) and electrical conductivity uniformity (resistivity). Detailed Implementation

[0026] The present invention will now be described and illustrated in detail with reference to the embodiments.

[0027] The raw materials used in the following examples and comparative examples are all commercially available products.

[0028] Example 1 Pre-treatment of raw materials Needle coke was added to a pot furnace and calcined at 1250℃ for 30 hours to obtain calcined coke. The quality indicators of the calcined coke were tested and found to be as follows: the true density of the needle coke was 2.17 g / cm³. 3 With a resistivity of 436 μΩ·m, the calcination of the raw materials is complete.

[0029] After passing inspection, the calcined coke is sequentially crushed by a jaw crusher (coarse crushing), a cone crusher (medium crushing), and a double roll crusher (fine crushing) to obtain granules with a particle size of 0.01~20mm. The granules are then screened at multiple stages to obtain granules A1 (particle size range 8mm≤A1<12mm), A2 (particle size range 4mm≤A2<8mm), A3 (particle size range 0.5mm≤A3<4mm), and A4 (particle size range 4mm≤A2<8mm). 4. A total of 4 granular grades (particle size range 0.01mm≤A4<0.5mm); a portion of granular material A4 is ground by Raymond mill to obtain powder with a particle size of 0.01mm≤D<0.15mm; the powder is then screened through multiple stages to obtain two powder grades: powder B1 (particle size range 0.075mm≤B1<0.15mm) and powder B2 (particle size range 0.01mm≤B2<0.075mm).

[0030] The graphene oxide and boric acid were mixed and ground in a mass ratio of 1:1.1. 120g of the resulting mixed powder was weighed, spread evenly, and pushed into the reactor. Ar gas was introduced to replace the air and the pressure was maintained. The temperature was raised according to the set program. First, it was heated to 220℃ and held for 20min. Then, it was heated to 400℃ and held at 12MPa for 60min. Ar was slowly removed from the reactor and the mixture was allowed to cool naturally to room temperature. The mixture was washed and filtered three times with hot distilled water at 70℃ to obtain boron-doped graphene.

[0031] Based on 1000g of iron oxide (powder), weigh out 90g of melamine, 180g of polyethylene glycol, 6000g of water, 80g of boron-doped graphene, and 90g of boric acid. Mix the weighed raw materials to obtain a functional loading liquid. The graded granules (A1, A2, A3, and A4) and powders (B1 and B2) obtained by grading and sieving are respectively loaded into different impregnation tanks at a mass ratio of 1:0.08 with the functional loading liquid. Loading is performed, and wet materials are obtained after loading. The wet materials are dried until the surface is dry and there is no obvious adhesion, resulting in loaded materials A1, A2, A3, A4, B1, and B2, completing the loading operation.

[0032] Preparation of graphite Weigh the required raw materials and mix them according to the following mass percentages: Loading agent A1 31%, Loading agent A2 16%, Loading agent A3 15%, Loading agent A4 6%, Loading agent B1 6%, Loading agent B2 4%, Coal tar pitch 20%, and Stearic acid 2.0%. Dry mix the dry materials of loading agent A1, A2, A3, A4, B1, B2, and stearic acid at 150℃ for 20 minutes; then add coal tar pitch and wet mix at -0.05MPa and 190℃ for 40 minutes to obtain a mixture. The mixture is observed to be a uniform paste, and no dry powder or lumps are observed when sampled. Cool the mixture to 105℃ within 25 minutes to complete the mixing operation.

[0033] After cooling, the mixture is fed into a horizontal hydraulic extruder and pre-pressed for 3 minutes at a pressure of 25 MPa to remove air from the mixture. Then, under the conditions of extrusion temperature of 130℃, extrusion pressure of 35 MPa, and extrusion speed of 150 mm / min, the mixture is extruded through a nozzle and the extruded green body is cut to a fixed length at the same time. The surface is observed to be smooth, without cracks, delamination, or pitting.

[0034] The green billets were fed into a roasting furnace and heated to 1200℃ according to the primary roasting heat treatment curve, held at that temperature for 16 hours, and then cooled before being removed from the furnace, completing the primary roasting. Surface impurities were removed, and the billets were impregnated with coal tar pitch before being fed back into the roasting furnace for a secondary roasting. The temperature was raised to 800℃ according to the secondary roasting heat treatment curve, held at that temperature for 5 hours, and then cooled before being removed from the furnace, completing the secondary roasting and obtaining the finished billets. The heat treatment curves for the primary and secondary roasting are shown in the table below:

[0035] The raw graphite blank is fed into an LWG furnace and heated to 1500℃ at a rate of 25℃ / h, and held at that temperature for 2 hours; then heated to 2200℃ at a rate of 3℃ / h, and held at that temperature for 2 hours; then heated to 2800℃ at a rate of 25℃ / h and held at that temperature for 12 hours. The furnace is then stopped and cooled. The finished graphite is obtained by machining the outer circle, end face, threads, and internal threaded holes.

[0036] The graphite body measures Φ600mm × 2400mm, and its bulk density is measured to be 1.72g / cm³. 3 It has a flexural strength of 13.9 MPa, an elastic modulus of 8.17 GPa, a resistivity of 3.51 μΩ·m, an ash content of ≤0.1%, and a coefficient of thermal expansion of 1.1 × 10⁻⁶. -6 / ℃.

[0037] Example 2 Pre-treatment of raw materials Needle coke was added to a pot furnace and calcined at 1300℃ for 25 hours to obtain calcined coke. The quality indicators of the calcined coke were as follows: true density of needle coke 2.19 g / cm³. 3 With a resistivity of 452 μΩ·m, the calcination of the raw materials is complete.

[0038] After passing inspection, the calcined coke is sequentially crushed by a jaw crusher (coarse crushing), a cone crusher (medium crushing), and a double roll crusher (fine crushing) to obtain granules with a particle size of 0.01~20mm. The granules are then screened at multiple stages to obtain granules A1 (particle size range 8mm≤A1<12mm), A2 (particle size range 4mm≤A2<8mm), A3 (particle size range 0.5mm≤A3<4mm), and A4 (particle size range 4mm≤A2<8mm). 4. A total of 4 granular grades (particle size range 0.01mm≤A4<0.5mm); a portion of granular material A4 is ground by Raymond mill to obtain powder with a particle size of 0.01mm≤D<0.15mm; the powder is then screened through multiple stages to obtain two powder grades: powder B1 (particle size range 0.075mm≤B1<0.15mm) and powder B2 (particle size range 0.01mm≤B2<0.075mm).

[0039] The graphene oxide and boric acid were mixed and ground in a mass ratio of 1:0.85. 120g of the resulting mixed powder was weighed, spread evenly, and pushed into the reactor. Ar gas was introduced to replace the air and the pressure was maintained. The temperature was increased according to the set program. First, it was heated to 200℃ and held for 25min. Then, it was heated to 430℃ and held at 15MPa for 50min. The Ar gas in the reactor was slowly removed and the mixture was allowed to cool naturally to room temperature. The mixture was washed and filtered three times with hot distilled water at 60℃ to obtain boron-doped graphene.

[0040] Based on 1000g of iron oxide (powder), weigh out 120g of melamine, 200g of polyethylene glycol, 7500g of water, 100g of boron-doped graphene, and 150g of boric acid. Mix the weighed raw materials to obtain a functional loading liquid. The graded granules (A1, A2, A3, and A4) and powders (B1 and B2) obtained by grading and sieving are respectively loaded into different impregnation tanks at a mass ratio of 1:0.09 with the functional loading liquid. Loading is performed, and wet materials are obtained after loading. The wet materials are dried until the surface is dry and there is no obvious adhesion, resulting in loaded materials A1, A2, A3, A4, B1, and B2, completing the loading operation.

[0041] Preparation of graphite Weigh the required raw materials and mix them according to the following mass percentages: Loading material A1: 28%, Loading material A2: 10%, Loading material A3: 18%, Loading material A4: 12%, Loading material B1: 10%, Loading material B2: 5.8%, Coal tar pitch (binder): 15%, and Stearic acid: 1.2%. Dry mix the dry materials (Loading materials A1, A2, A3, A4, B1, B2, and stearic acid) at 140℃ for 25 minutes. Then add the coal tar pitch and wet mix at -0.08MPa and 170℃ for 55 minutes to obtain a mixture. The mixture is observed to be a uniform paste. Samples are taken for observation and no dry powder or lumps are found. Cool the mixture to 120℃ within 20 minutes to complete the mixing operation.

[0042] After cooling, the mixture is fed into a horizontal hydraulic extruder and pre-pressed for 4 minutes at a pressure of 18 MPa to remove air from the mixture. Then, the mixture is extruded through a nozzle at an extrusion temperature of 120℃, an extrusion pressure of 32 MPa, and an extrusion speed of 50 mm / min. The extruded green body is cut to a fixed length at the same time. The surface is observed to be smooth, without cracks, delamination, or pitting.

[0043] The green billets are fed into a roasting furnace and heated to 1200℃ according to the primary roasting heat treatment curve, held at that temperature for 12 hours, and then cooled before being removed from the furnace, completing the primary roasting. Impurities adhering to the surface are removed, and the billets are impregnated with coal tar pitch before being fed back into the roasting furnace for a secondary roasting. The temperature is raised to 800℃ according to the secondary roasting heat treatment curve, held at that temperature for 8 hours, and then cooled before being removed from the furnace, completing the secondary roasting and obtaining the finished billets. The heat treatment curves for the primary and secondary roasting are shown in the table below:

[0044] The raw material is fed into an LWG furnace and heated to 1500℃ at a rate of 20℃ / h, and held at that temperature for 1.5h; then heated to 2200℃ at a rate of 8℃ / h, and held at that temperature for 5h; finally, heated to 2800℃ at a rate of 30℃ / h and held at that temperature for 15h. The furnace is then stopped and cooled. The finished graphite is obtained by machining the outer circle, end face, threads, and internal threaded holes.

[0045] The graphite body measures Φ600mm × 2400mm, and its bulk density is measured to be 1.73g / cm³. 3 It has a flexural strength of 14.2 MPa, an elastic modulus of 8.13 GPa, a resistivity of 3.48 μΩ·m, an ash content of ≤0.1%, and a coefficient of thermal expansion of 1.1 × 10⁻⁶. -6 / ℃.

[0046] Example 3 Pre-treatment of raw materials Needle coke was added to a pot furnace and calcined at 1350℃ for 20 hours to obtain calcined coke. The quality indicators of the calcined coke were as follows: true density of needle coke 2.20 g / cm³. 3 With a resistivity of 441 μΩ·m, the calcination of the raw materials is complete.

[0047] After passing inspection, the calcined coke is sequentially crushed by a jaw crusher (coarse crushing), a cone crusher (medium crushing), and a double roll crusher (fine crushing) to obtain granules with a particle size of 0.01~20mm. The granules are then screened at multiple stages to obtain granules A1 (particle size range 8mm≤A1<12mm), A2 (particle size range 4mm≤A2<8mm), A3 (particle size range 0.5mm≤A3<4mm), and A4 (particle size range 4mm≤A2<8mm). 4. A total of 4 granular grades (particle size range 0.01mm≤A4<0.5mm); a portion of granular material A4 is ground by Raymond mill to obtain powder with a particle size of 0.01mm≤D<0.15mm; the powder is then screened through multiple stages to obtain two powder grades: powder B1 (particle size range 0.075mm≤B1<0.15mm) and powder B2 (particle size range 0.01mm≤B2<0.075mm).

[0048] The graphene oxide and boric acid were mixed and ground in a mass ratio of 1:1.8. 120g of the resulting mixed powder was weighed, spread evenly, and pushed into the reactor. Ar gas was introduced to replace the air and the pressure was maintained. The temperature was raised according to the set program. First, it was heated to 190℃ and held for 30min. Then, it was heated to 420℃ and held at 13MPa for 55min. Ar was slowly removed from the reactor and the mixture was allowed to cool naturally to room temperature. The mixture was washed and filtered three times with hot distilled water at 80℃ to obtain boron-doped graphene.

[0049] Based on 1000g of iron oxide (powder), weigh out 100g of melamine, 120g of polyethylene glycol, 8000g of water, 120g of boron-doped graphene, and 180g of boric acid. Mix the weighed raw materials to obtain a functional loading liquid. The graded granules (A1, A2, A3, and A4) and powders (B1 and B2) obtained by grading and sieving are respectively loaded into different impregnation tanks at a mass ratio of 1:0.1 with the functional loading liquid. Loading is performed, and wet materials are obtained after loading. The wet materials are dried until the surface is dry and there is no obvious adhesion, resulting in loaded materials A1, A2, A3, A4, B1, and B2, completing the loading operation.

[0050] Preparation of graphite Weigh the required raw materials and mix them according to the following mass percentages: Loading material A1 32%, Loading material A2 12%, Loading material A3 16%, Loading material A4 7.5%, Loading material B1 8%, Loading material B2 8%, Coal tar pitch binder 15%, and Stearic acid 1.5%. Dry mix the dry materials (Loading materials A1, A2, A3, A4, B1, B2, and Stearic acid) at 120℃ for 35 minutes; then add the coal tar pitch and wet mix at -0.06MPa and 180℃ for 50 minutes to obtain a mixture. The mixture is observed to be a uniform paste, and no dry powder or lumps are observed. Cool the mixture to 90℃ within 30 minutes to complete the mixing operation.

[0051] After cooling, the mixture is fed into a horizontal hydraulic extruder and pre-pressed for 5 minutes at a pressure of 15 MPa to remove air from the mixture. Then, the mixture is extruded through a nozzle at an extrusion temperature of 140℃, an extrusion pressure of 20 MPa, and an extrusion speed of 120 mm / min. The extruded green body is cut to a fixed length at the same time. The surface is observed to be smooth, without cracks, delamination, or pitting.

[0052] The green billets are fed into a roasting furnace and heated to 1200℃ according to the primary roasting heat treatment curve, held at that temperature for 20 hours, and then cooled before being removed from the furnace, completing the primary roasting. Surface impurities are removed, and the billets are impregnated with coal tar pitch before being fed back into the roasting furnace for a secondary roasting. The temperature is raised to 800℃ according to the secondary roasting heat treatment curve, held at that temperature for 7 hours, and then cooled before being removed from the furnace, completing the secondary roasting and obtaining the finished billets. The heat treatment curves for the primary and secondary roasting are shown in the table below:

[0053] The molten graphite is fed into an LWG furnace and heated to 1500℃ at a rate of 15℃ / h, held at that temperature for 1 hour; then heated to 2200℃ at a rate of 6℃ / h, held at that temperature for 3.5 hours; and finally heated to 2800℃ at a rate of 20℃ / h, held at that temperature for 8 hours. The furnace is then stopped and cooled. The finished graphite is obtained by machining the outer diameter, end face, threads, and internal threaded holes.

[0054] The graphite body measures Φ600mm × 2400mm, and its bulk density is measured to be 1.72g / cm³. 3 It has a flexural strength of 14.6 MPa, an elastic modulus of 8.21 GPa, a resistivity of 3.55 μΩ·m, an ash content of ≤0.1%, and a coefficient of thermal expansion of 1.2 × 10⁻⁶. -6 / ℃.

[0055] Comparative Example 1 Without adding boron-doped graphene, the remaining operations are the same as in Example 1, to obtain the finished graphite with a graphite body size of Φ600mm×2400mm.

[0056] Comparative Example 2 Without adding melamine, the remaining operations are the same as in Example 1, to obtain the finished graphite with a graphite body size of Φ600mm×2400mm.

[0057] Comparative Example 3 Without adding polyethylene glycol, the remaining operations are the same as in Example 1, to obtain the finished graphite with a graphite body size of Φ600mm×2400mm.

[0058] Comparative Example 4 Without adding boric acid, the remaining operations are the same as in Example 1, to obtain the finished graphite with a graphite body size of Φ600mm×2400mm.

[0059] The performance data of comparative examples 1 to 4 are shown in Table 1.

[0060] Table 1 Comparative Graphite Performance Data

Claims

1. A graphite production process, characterized in that, Includes the following steps: (1) The raw material needle coke is calcined and then crushed and screened to obtain granules and powders of different particle sizes; A functional loading liquid was prepared by independently mixing granules and powders of different particle sizes with the functional loading liquid to obtain loading materials of various grades; the functional loading liquid included expansion inhibitors and boron-doped graphene. (2) The load-bearing materials, binders and lubricants of each grade are mixed to obtain a mixture; (3) The mixture is extruded to form a green body; (4) The raw blanks are baked to obtain cooked blanks; (5) The molten blank is graphitized and then processed into graphite.

2. The graphite production process according to claim 1, characterized in that, In step (1), the calcination temperature is 1250~1350℃, and the calcination time is 20~30h; after calcination, the true density of the needle coke is ≥2.12g / cm³. 3 Resistivity ≤ 500 μΩ·m.

3. The graphite production process according to claim 1, characterized in that, In step (1), after crushing and screening, four granular grades, namely granules A1, A2, A3 and A4, and two powder grades, namely powder B1 and B2, are obtained. The particle size range of granules A1 is 8mm≤A1<12mm, the particle size range of granules A2 is 4mm≤A2<8mm, the particle size range of granules A3 is 0.5mm≤A3<4mm, and the particle size range of granules A4 is 0.01mm≤A4<0.5mm. The particle size range of powder B1 is 0.075mm≤B1<0.15mm, and the particle size range of powder B2 is 0.01mm≤B2<0.075mm.

4. The graphite production process according to claim 1, characterized in that, In step (1), the expansion inhibitor is iron oxide, and the functional loading liquid also includes melamine, polyethylene glycol, boric acid and water; based on 100 parts by mass of iron oxide, melamine is 9-12 parts, polyethylene glycol is 12-20 parts, boric acid is 9-18 parts, boron-doped graphene is 8-12 parts and water is 600-800 parts; among which, boron-doped graphene is prepared by grinding graphene oxide and boric acid, followed by two heat treatments and washing, with a mass ratio of graphene oxide to boric acid of 1:0.85-1.8, the first heat treatment temperature is 190-220℃, the first heat treatment time is 20-30 min; the second heat treatment temperature is 400-430℃, the second heat treatment pressure is 12-15 MPa, and the second heat treatment time is 50-60 min.

5. The graphite production process according to claim 3, characterized in that, In step (1), granules and powders of different particle sizes are independently mixed with functional loading liquid at a mass ratio of 1:0.08~0.1 and then loaded; granules A1, A2, A3, A4, powder B1 and powder B2 are independently mixed with functional loading liquid and loaded to obtain loaded materials A1, A2, A3, A4, B1 and B2.

6. The graphite production process according to claim 5, characterized in that, In step (2), the binder is coal tar pitch and the lubricant is stearic acid. The composition of the ingredients by mass percentage is as follows: load material A1 accounts for 28~32wt%, load material A2 accounts for 10~16wt%, load material A3 accounts for 15~18wt%, load material A4 accounts for 6~12wt%, load material B1 accounts for 6~10wt%, load material B2 accounts for 4~8wt%, coal tar pitch accounts for 15~20wt%, and stearic acid accounts for 1.2~2.0wt%.

7. The graphite production process according to claim 1, characterized in that, In step (2), the mixing includes dry mixing and wet mixing in sequence. The temperature of dry mixing is 120~150℃ and the dry mixing time is 20~35min. The pressure of wet mixing is -0.08~-0.05MPa, the wet mixing temperature is 170~190℃ and the wet mixing time is 40~55min. After wet mixing, the material is cooled down to 90~120℃ within 20~30min.

8. The graphite production process according to claim 1, characterized in that, In step (3), the material is pre-pressed at 15-25 MPa for 3-5 minutes before extrusion molding; the extrusion temperature is 120-140℃, the extrusion pressure is 20-35 MPa, and the extrusion speed is 50-150 mm / min.

9. The graphite production process according to claim 1, characterized in that, In step (4), roasting includes primary roasting and secondary roasting after impregnation with coal tar pitch; during primary roasting, the temperature is raised to 1200℃ and held for 12~20h; during secondary roasting, the temperature is raised to 800℃ and held for 5~8h.

10. The graphite production process according to claim 1, characterized in that, In step (5), graphitization is carried out in an LWG furnace with gradient heating. The gradient heating process is as follows: heating to 1500℃ at a heating rate of 15~25℃ / h and holding at that temperature for 1~2h; then heating to 2200℃ at a heating rate of 3~8℃ / h and holding at that temperature for 2~5h; finally heating to 2800℃ at a heating rate of 20~30℃ / h and holding at that temperature for 8~15h.

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